1. Field of the Invention
The present invention relates to a method for recycling of plating solutions by removing one metallic material from an alloy plating solution containing two kinds of metallic materials which differ in standard electrode potential, and preparing a single metal plating solution substantially from the remaining other metallic material.
2. Related Art
When coated with a plating film of Sn alone or Sn alloy, conductive materials such as leads or lead frames can have excellent conductivity and mechanical strength. The conductive materials can also have the corrosion resistance and excellent solderability that are possessed by Sn alone or Sn alloy. For these features, the conductive members are often used in the field of electric and electronic devices such as various terminals, connectors, and leads, and the field of electric power cables.
On the other hand, when semiconductor chips are mounted on circuit boards, the outer lead parts of the semiconductor chips are coated with plated films so as to improve their solderability. A typical example of these plated films is soldering (Sn—Pb alloy) which is widely used for its excellent solderability, corrosion resistance, and other preferable properties.
As described above, one of the most popular conventional plating solutions is Sn—Pb alloy plating solutions. However, in recent years, the influence of lead on the environment and humans has been drawing attention and use of Sn—Pb alloy plating solutions containing lead has been on the decline globally or withdrawn from service. Consequently, at the same time, the Sn—Pb alloy plating solutions have come to be replaced by Sn—Bi alloy plating solutions which can provide the same level of qualities. At the same time, there are also shifts towards new alloy plating solutions of Sn—Cu alloy, Sn—Ag alloy, Sn—In alloy, Sn—Zn alloy, and the like.
As described above, on the market, in consideration of the adverse affect of lead on the environment and humans, a shift toward plating solutions not containing lead is an urgent necessity. And a shift toward Sn—Bi alloy plating solutions which are stable in quality and plating techniques has made advancements.
On the other hand, there is a concern about the influence of Bi on the environment and humans and the toxicity of Bi. To be more specific, Bi itself exists as a mineral, and can also be obtained as a by-product in the production of lead. With fears that Bi maybe poisonous like lead, there is a concern that dumping Bi-containing plating solutions may affect the environment and humans as described above.
In semiconductor chips, the outer lead parts of the semiconductor chips are coated with plating films made from Sn—Bi alloy plating solutions so as to improve their solderability, corrosion resistance, and other properties, and then are mounted on circuit boards. At this time, the lead contained in the soldering during mounting and the Bi inside the plating films have the properties to facilitate the formation of a low-temperature alloy. The mounting region is vulnerable to heat stress for its structural feature, which causes a problem that the low-temperature alloy may decrease the mounting reliability.
In the recycling of conductive members, the Bi contained in the plating films that have been applied to their surfaces sometimes deposit by a fixed amount on the conductive members and remain there. In such a case, Bi exists in the recycled materials, which may induce a decrease in the strength of the recycled materials.
In the aforementioned situation, in the plating solutions market, there is a growing demand for a shift towards Sn plating solutions not containing a second metal such as Bi, and it is becoming necessary to make a shift towards plating solutions of Sn which is a substantially single metal as the plating solutions of a second generation.
In the plating solutions market, with the shift towards the Sn—Bi alloy plating solutions which are lead-free plating solutions as the first generation plating solutions, the conventional Sn—Pb alloy plating solutions are dumped or subjected to an effluent treatment, while Sn—Bi alloy plating solutions are newly mixed and prepared. In the preparation for the plating solutions of a second generation, the Sn—Bi alloy plating solutions used for the present plating can be dumped or subjected to an effluent treatment in the same manner, and Sn plating solutions can be newly mixed and prepared.
However, the shift towards Sn plating solutions following the shift from Sn—Pb alloy plating solutions to Sn—Bi alloy plating solutions involves a large amount of environmental loads, such as use of chemicals and an effluent treatment, and also involves the cost for the effluent treatment. On the other hand, it is necessary to newly purchase plating chemicals, thereby making the cost of manufacturing enormous.
In addition, newly preparing Sn plating solutions requires learning the know-how cultivated while the Sn—Bi alloy plating solutions are in use, such as chemical concentration control, electrodeposition ratio, plating techniques including plating film composition, and analysis technique, which consumes a great amount of time and cost. It is also necessary to newly install a production line for a plating treatment, which makes it harder to utilize the present facilities, thereby also requiring the cost of equipment.